This invention relates to an object lens supporting unit for supporting an object lens, in particular, to the unit capable of compensating for inclination of the object lens when an optical and electrical apparatus provided with the object lens is manufactured.
Generally, the object lens supporting unit is applied in an optical disk drive for reading/writing data from/to an optical recording medium of disk type by irradiating laser beam to the medium and optically sensing reflected laser beam from the medium/by irradiating laser beam to the medium. The object lens supporting unit is driven in such direction that traverse innumerable tracks formed on the optical medium and is stopped on a target track. Thus, the unit carried out to irradiate the track and to read/write data from/to the track.
Conventionally, to compensate for the inclination of the object lens, various remedies have been contrived. Basically, to compensate for the inclination of the object lens, it requires a mechanism for adjusting inclination of the object lens and mechanisms for compensating for distance deviation of the object lens in focusing and tracking directions caused by the adjusting of inclination of the objects lens. Herein, the focusing direction is a direction vertical to a recording surface on a disc type-recording medium, while the tracking direction is a direction transverse recording tracks formed on the recording medium. Therefore, the conventional structure for compensating for the inclination fo the object lens is complex in structure.
To settle matter mentioned above, an object lens supporting unit related to this invention is disclosed in Japanese Patent Unexamined Publication (A) No. 223953/1984.
The unit uses a concave pedestal for adjusting the inclination of the object lens in an object lens drive. The unit comprises a supporting base for supporting the object lens and a head case for supporting the supporting thereon. The supporting base is provided with convex and spherical parts on a bottom surface thereof. The head case is provided with the concave pedestal on an upper surface thereof. The concave pedestal has a concave surface along a spherical surface of an imaginary or a supposed sphere drawn around a principal point of the object lens as central point. In other words, the concave surface has a supposed central point which positionally coincides with the principal point of the object lens. Since the supporting base is supported on the head case through only the convex and spherical parts, the convex and spherical parts can be slid on the spherical surface of the concave pedestal. Therefore, the entire supporting base can be tilted in every direction around the principal point of the object lens. This structure has an advantage that the principal point of the object lens is almost invariable in position. It is therefore unnecessary to compensate for distance deviation of the object lens in focusing and tracking directions after the object lens was adjusted for the inclination thereof.
However, it is difficult for this structure to reduce in thickness because the head case requires a relatively large thickness in order to secure a space for forming the spherical surface of the concave pedestal. If optical system of this structure is reduced in height with the structure maintained basically, it becomes difficult to put the supposed central point of the concave pedestal onto the principal point of the object lens. Namely, if it is required to reduce a height size as a first priority in the structure, the object lens deviates in the focusing and/or the tracking directions when it was adjusted the inclination. In the event, the above-mentioned advantage is spoiled. As described above, the related technique is practically unsuitable to reduce in height and to apply into apparatuses such as portable or mobile computers requested to reduce in height.